The present invention relates to large area, flat cathodoluminescent image display devices; and particularly to apparatus for modulating such display devices.
Flat large area cathodoluminescent display devices have been suggested for use in image displays, such as television. These devices may have a matrix of individually addressable electron sources formed by electron multipliers operating in a regenerative feedback mode. Such devices have a cathode at one end of an electron multiplier and a cathodoluminescent screen at the other end. The electrons from the cathode enter the multiplier which amplifies the electron flow. Modulating, focusing and accelerating electrodes are between the multiplier and the screen to shape the electron beam and accelerate it toward the screen. The screen is coated with phosphor material which emits light upon electron bombardment. The output of the electron multiplier also generates a feedback species, such as positive ions. These positive ions in the display device travel back to and strike the cathode emitting secondary electrons and completing a feedback loop so as to allow sustained electron emission.
The individual electron sources for the display device are intrinsically nonuniform in their output because of unavoidable variations in the multiplier dimensions and secondary emission properties. Therefore, the light output from the phosphor material may vary from one area of the screen to another. In addition, the flow of electrons from each multiplier must be modulated to provide the proper brightness for the corresponding picture element. Therefore, a means of unifying and modulating the output of the electron sources is required if such display devices are to be utilized for image display applications, such as television, where a high degree of uniformity and gray scale control are required.